The present disclosure relates to the oil and gas industry and, more particularly, to real-time optical flow imaging of wellbore fluids.
During the drilling and completion of a hydrocarbon-producing well, various wellbore fluids are circulated in and/or out of the well. Such wellbore fluids include, but are not limited to, drilling fluids, drill-in fluids, completion fluids, fracturing fluids, and work-over fluids. While drilling a wellbore, for example, a drilling fluid or “mud” is continuously circulated from a surface location down to the bottom of the wellbore being drilled and back to the surface again. Drilling fluids often include a plurality of particles that impart specific properties (e.g., viscosity, mud weight, and the like) and capabilities (e.g., wellbore strengthening) to the drilling fluid.
Prior to being conveyed downhole, the drilling fluid may be treated by adding or removing various components to obtain a predetermined drilling fluid mixture designed for optimal efficiency of the drilling fluid. Weighting agents, for example, are often added to the drilling fluid to produce a drilling fluid with a desired mud weight (i.e., density). Weighting agents are particles having a specific gravity greater than the base fluid of the drilling fluid and, therefore, are able to affect the equivalent circulating density (ECD) of the drilling fluid. During drilling operations, the ECD is often carefully monitored and controlled relative to the fracture gradient of the subterranean formation. Typically, the ECD during drilling is close to the fracture gradient without exceeding it, and when the ECD exceeds the fracture gradient, a fracture may form in the subterranean formation and drilling fluid may be lost into the formation (often referred to as lost circulation).
Due to natural tendencies, the physical characteristics of the drilling fluid mixture introduced downhole may change during circulation and thereby result in a different particle size distribution (PSD) of drilling fluid components. For example, PSD can change due to the addition of fines or cuttings entrained in the drilling fluid during drilling. Moreover, drilling fluid components are subject to particle size attrition resulting from particles breaking down or otherwise being ground to smaller sizes while circulating through the wellbore. As the particle sizes change, the PSD of the drilling fluid is correspondingly altered. In other cases, drilling fluid components of a certain size may be lost through pores defined in the wellbore wall, and thereby also alter the PSD of the drilling fluid. To counteract such losses, lost circulation materials (LCM) are often added to the drilling fluid mixture to form a filter cake on the wellbore wall and otherwise prevent drilling fluid components from escaping into wellbore pores and/or fissures. Adding the LCM, however, alters the PSD of the drilling fluid, and some LCM compositions are removed from the drilling fluid during operation due to intended consumption or using shaker screens or other solids control units.